The present invention relates to a control system for cameras provided with an electronically controlled focal-plane shutter.
An integrated circuit for electronically controlling an instant picture camera in which an electronic shutter mechanism and an aperture mechanism are controlled by a single output solenoid is known well from 1977 IEEE International Solid-State Circuits Conference DIGEST OF TECHNICAL PAPERS p214-p215 T. M. Frederksen et al "A Single-Chip, All Bipolar, Camera Control IC".
It is necessary in a TTL (Through The Lens) type single lens reflex camera, which permits an accurate exposure by measuring the light passed through the lens in the light path in the camera body without considering the correction coefficient of lens filter, that a shutter mechanism and an aperture mechanism be controlled independently of each other. The electronic shutter for this TTL type single lens reflex camera is a focal-plane shutter having a front shutter blind for exposing the film and a rear shutter blind for screening the light. Both of these shutter blinds are mechanically held at once when the film is wound up.
In an automatically controlled camera, in which the iris value or shutter speed is electronically calculated and controlled with reference to a measured light value, an electric power is supplied into an automatic control circuit therein when a shutter button is depressed, to calculate the iris value or shutter speed on the basis of input information including measured light value and memorize the calculated value. The film is thereafter exposed under the memorized conditions. The exposure time for the film, i.e. the shutter speed is determined by the difference between the time of sliding movement of the front shutter blind and the time of sliding movement of the rear shutter blind. The sliding of the front and rear shutter blinds is carried out by mechanically releasing the shutter blinds mechanically retained.
In a conventional automatically controlled camera, a voltage from a battery inside the camera is supplied into an automatic control circuit through a mechanical operation of a power switch. Namely, a mechanical power switch is turned on when a first release switch of a two-step release switch (light measuring switch) is turned on, to start supplying a battery voltage into the automatic control circuit. When a second release switch (shutter switch) is turned on, a shutter action is made as the rear shutter blind is slided. After the shutter action has been finished, the first release switch is turned off so that the mechanical power switch is turned off to stop the supply of battery voltage into the automatic control circuit.
In order to start and stop the supply of battery voltage into the automatic control circuit in a conventional automatically controlled camera, it is necessary that the mechanical power switch be turned on and off in accordance with the operations of the mechanical two-step release switch. Then, the construction of the mechanical power switch becomes complicated and the operations of the switch are not reliable.